Sus-an Membrane

The Sus-an Membrane, also called the Hibernator or the Suspended Animation Membrane, is the 12th of the 19 genetically-engineered organs created from a Space MarineChapter's gene-seed that is implanted into a normal human adolescent male to transform him into a Neophyte of an Adeptus AstartesChapter. Initially implanted within the Neophyte's cranium, this organ eventually produces a membrane comprised of genetically-engineered neural tissue that merges with the recipient's cerebrum, becoming a full part of his neural architecture.

The organ's functions are ineffective without follow-up chemical therapy and training by a Chapter's Apothecaries, but with sufficient practice and instruction a Space Marine can use this implant to enter a state of suspended animation, consciously or as an automatic reaction to extreme trauma, keeping the Space Marine alive for many standard years, even if he has suffered otherwise mortal wounds. Only the appropriate chemical therapy or hypnotic auto-suggestion can revive a Space Marine from this state.

The longest recorded period spent in suspended animation was undertaken by Battle-Brother Silas Err of the Dark AngelsChapter, who was revived after 567 standard years in Sus-an hibernation. However, the Dark Angels SergeantAbdaziel Magron is known to have survived in Sus-an hibernation following his ejection into the vacuum of space during a void battle between the Dark Angels and the World EatersLegions until being reawakened by one of the Fallen Angels in the late 41st Millennium.

This represents a period in hibernation of over ten thousand standard years. However, this extraordinary feat is not known amongst the Adeptus Astartes or the Adeptus Mechanicus due to the secretive nature of the Dark Angels Chapter, and the reality that Magron fell into heresy and the service of the Blood God Khorne soon after his awakening.

Magron eventually repented and turned himself over to his brethren for judgment, and his life was mercifully ended at the Dark Angels fortress-monastery, The Rock. Because of his fall from grace, Magron's very existence is kept as yet another secret of the Dark Angels which they share neither with their fellow Space Marines or the Imperium at large.

Sources

Codex Adeptus Astartes - Space Marines (8th Edition), pp. 10-11

Codex: Black Templars (4th Edition), pg. 10

Codex: Space Marines (5th Edition), "The Making of a Space Marine," pg. 10